The principle of vaccination has been known since the 18th century in the form of empirical treatment against smallpox. The first scientific vaccine was developed by Pasteur (rabies). This was a first generation vaccine, as was the smallpox vaccine, using live animals for production. Second generation vaccines are produced in eggs (Influenza, Yellow fever) and third generation vaccines are produced in cell culture (Polio, Measles, Rubella, Mumps, Tickborne encephalitis). Fourth generation vaccines are produced in various expression systems by recombinant DNA technology and are represented by hepatitis B virus surface antigen (HBsAg).
A vaccine can consist of the whole microorganism (bacteria, virus, parasite etc.) or its part (subunit vaccine). In the former case the microorganism is either inactivated (killed) or attenuated. In addition, as mentioned above, recombinant antigens or synthetic immunogenic peptides have been used recently and DNA vaccines have been developed relying on the host cell to produce the desired antigen(s).
The primary purpose of vaccination is and always has been prophylactic—prevention of particular disease.
Nevertheless, even relatively speedy development of vaccines against some life-threatening diseases may be too late for people already infected. The number of people infected worldwide with three of the most common human viruses—hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV) represents up to 10% of human population when the latest figures of 300-400 million for HBV, more than 60 million for HCV and more than 30 million for HIV are combined. There is thus a clear need for therapeutics and one of the options is development of therapeutic vaccines.
Vaccine development is expensive and the cost of developing a vaccine is between $US 50 million and 200 million. Much of the cost reflects efforts to make sure that a variety of antigenic variants of the particular infectious agent are disarmed by the vaccine. This is difficult with moderately genetically divergent microorganisms but it is almost impossible with viruses having antigens as variable as the surface glycoproteins of HIV, HCV or influenza. On the other hand, there are highly successful vaccines with a proven record of efficacy and safety, such as polio and measles, mumps and rubella (MMR). The main difference between HCV, HIV and influenza on the one hand and polio, measles, mumps and rubella on the other hand is that members of the latter group against which there are successful vaccines are genetically much more stable than the former group.
Influenza vaccination is targeted each season at particular variants which are predicted to appear based on epidemiological studies. Experimental HIV vaccines are based on various constructs of envelope protein(s) originating from one or several strains. However, it is still unlikely that this approach will be effective for the entire spectrum or at least a majority of worldwide field isolates. There is no vaccine in trials for HCV yet.
In contrast, as mentioned earlier viruses such as measles are genetically more stable. Vaccine strains induce broadly cross-reactive antibodies. Measles hemagglutinin (MeaH) is a major target of these antibodies. It is a glycoprotein as is the second surface protein—fusion protein (F). Both of them are required for a fusion of cell membranes, but the sequence of events starts with MeaH binding to the cell receptor, thought to be CD46. MeaH is a membrane anchored protein with amino acids 1 to 34 proposed to form a cytoplasmic domain, while 35 to 58 comprise a transmembrane domain (see FIG. 1). Residues 59 to 181 are thought to form a stalk, part of which (135 to 181) probably forms a hinge of a molecule [Sato et al., J. Virol. 69, 513-516 (1995)1. Spikes of MeaH on virion surface consist of tetramers (dimers of disulfide bridge-linked homodimers). Cysteines 139 and 154 were suggested to participate in intermolecular disulfide bonding between monomeric MeaH glycoproteins. Soluble forms resulting from endoproteinase digestion of measles virus particles all reacted with monoclonal antibodies suggesting the preservation of antigenicity/reactivity [Sato et al., J. Virol. 69, 513-516 (1995)]. MeaH domain required for hemadsorption and hemagglutination activities was mapped between residues 451 and 505 [Hummel & Bellini, J. Virol. 69, 1913-1916 (1995)]. In addition to hemadsorption, the mutagenesis Val451Glu and Tyr481Asn also abrogated CD46 downregulation and HeLa cell fusion [Lecouturier et al., J. Virol. 70, 4200-4204 (1996)]. A novel site required for CD46 interaction was mapped between 473 and 477 [Patterson et al., Virology 256, 142-151 (1999)]. Additional neutralizing epitope NE244-250, located next to CD46 downregulating amino acid Arg 243, may be involved in CD46 binding [Fournier et al., J. Gen. Virol. 78, 1295-1302 (1997)].
It is an object of the present invention to provide a therapy for people infected with genetically variable viruses and other therapeutic targets.